3D imaging apparatuses are used for obtaining not only image information of an object but also a range image—that is an image which shows the 3D characteristics and range information of an object. Exemplary applications of such 3D imaging apparatuses include automotive obstacle-detection systems, robotically assisted surgical systems, and gesture recognition systems for arcade games.
One of typical and disclosed imaging techniques for the 3D imaging apparatus is to obtain a range image by emitting intensity-modulated light to an object (typically infrared light) and measuring for each pixels a time period for the emitted light to come back from the object (time of flight or TOF). This technique is referred to as the TOF depth measurement.
Specifically, the TOF depth measurement is applied to 3D imaging cameras (also referred to as TOF camera). A TOF camera emits to an object light modulated so that the light intensity decreases as the time elapses, and obtains the light bounced on the object with predetermined shutter timing or a time period while the shutter is opening. In such a camera, the emitted light is modulated so that the intensity of the light decreases over time. Thus, as the range between the camera and the object is shorter, the time-of-flight of the light (the time that elapses when the light emitted from the camera bounces on the object and travels back to the camera) is shorter. Accordingly, the amount of the emitted light does not decrease much, and the intensity of the emitted light is high. In contrast, as the range between the camera and the object is longer, the time-of-flight of the light is longer. Accordingly, the amount of the emitted light decreases much, and the intensity of the emitted light is low. Hence, the intensity of the light received by each of the pixels is higher as the range to the object is shorter, and, based on the intensity of the received light for each pixel, information on the range to the object is provided as the brightness of the object.
Patent Literature 1 discloses an imaging technique other than the TOF depth measurement. The technique is to obtain a 3D image of an object with no light emitted to the object. Specifically, the technique utilizes two cameras placed in parallel at a predetermined interval to obtain an object, and searches for corresponding pixels (stereo matching) between the obtained two images (a base image obtained by a base camera and a reference image obtained by a reference camera). Then, a difference of corresponding parts on the object images is measured by the principle of triangulation, and a range image of the object is obtained. This is how the stereo matching works. Moreover, in addition to the two cameras for the stereo matching. Patent Literature 1 proposes a 3D imaging apparatus including an additional TOF camera separately located from the two cameras.